incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Laing, Michael" <michael.la...@nytimes.com>
Subject Re: Exactly one wide row per node for a given CF?
Date Tue, 10 Dec 2013 17:17:54 GMT
You could shard your rows like the following.

You would need over 100 shards, possibly... so testing is in order :)

Michael

-- put this in <file> and run using 'cqlsh -f <file>

DROP KEYSPACE robert_test;

CREATE KEYSPACE robert_test WITH replication = {
    'class': 'SimpleStrategy',
    'replication_factor' : 1
};

USE robert_test;

CREATE TABLE bdn_index_pub (
    tree int,
    shard int,
    pord int,
    hpath text,
    PRIMARY KEY ((tree, shard), pord)
);

-- shard is calculated as pord % 12

COPY bdn_index_pub (tree, shard, pord, hpath) FROM STDIN;
1, 1, 1, "Chicago"
5, 3, 15, "New York"
1, 5, 5, "Melbourne"
3, 2, 2, "San Francisco"
1, 3, 3, "Palo Alto"
\.

SELECT * FROM bdn_index_pub
WHERE shard IN (0,1,2,3,4,5,6,7,8,9,10,11)
    AND tree =  1
    AND pord < 4
    AND pord > 0
ORDER BY pord desc
;

-- returns:

-- tree | shard | pord | hpath
--------+-------+------+--------------
--    1 |     3 |    3 |  "Palo Alto"
--    1 |     1 |    1 |    "Chicago"



On Tue, Dec 10, 2013 at 8:41 AM, Robert Wille <rwille@fold3.com> wrote:

> I have a question about this statement:
>
> When rows get above a few 10’s  of MB things can slow down, when they get
> above 50 MB they can be a pain, when they get above 100MB it’s a warning
> sign. And when they get above 1GB, well you you don’t want to know what
> happens then.
>
> I tested a data model that I created. Here’s the schema for the table in
> question:
>
> CREATE TABLE bdn_index_pub (
>
> tree INT,
>
> pord INT,
>
> hpath VARCHAR,
>
> PRIMARY KEY (tree, pord)
>
> );
>
> As a test, I inserted 100 million records. tree had the same value for
> every record, and I had 100 million values for pord. hpath averaged about
> 50 characters in length. My understanding is that all 100 million strings
> would have been stored in a single row, since they all had the same value
> for the first component of the primary key. I didn’t look at the size of
> the table, but it had to be several gigs (uncompressed). Contrary to what
> Aaron says, I do want to know what happens, because I didn’t experience any
> issues with this table during my test. Inserting was fast. The last batch
> of records inserted in approximately the same amount of time as the first
> batch. Querying the table was fast. What I didn’t do was test the table
> under load, nor did I try this in a multi-node cluster.
>
> If this is bad, can somebody suggest a better pattern? This table was
> designed to support a query like this: select hpath from bdn_index_pub
> where tree = :tree and pord >= :start and pord <= :end. In my application,
> most trees will have less than a million records. A handful will have 10’s
> of millions, and one of them will have 100 million.
>
> If I need to break up my rows, my first instinct would be to divide each
> tree into blocks of say 10,000 and change tree to a string that contains
> the tree and the block number. Something like this:
>
> 17:0, 0, ‘/’
> …
> 17:0, 9999, ’/a/b/c’
> 17:1,10000, ‘/a/b/d’
> …
>
> I’d then need to issue an extra query for ranges that crossed block
> boundaries.
>
> Any suggestions on a better pattern?
>
> Thanks
>
> Robert
>
> From: Aaron Morton <aaron@thelastpickle.com>
> Reply-To: <user@cassandra.apache.org>
> Date: Tuesday, December 10, 2013 at 12:33 AM
> To: Cassandra User <user@cassandra.apache.org>
> Subject: Re: Exactly one wide row per node for a given CF?
>
> But this becomes troublesome if I add or remove nodes. What effectively I
>> want is to partition on the unique id of the record modulus N (id % N;
>> where N is the number of nodes).
>
> This is exactly the problem consistent hashing (used by cassandra) is
> designed to solve. If you hash the key and modulo the number of nodes,
> adding and removing nodes requires a lot of data to move.
>
> I want to be able to randomly distribute a large set of records but keep
>> them clustered in one wide row per node.
>
> Sounds like you should revisit your data modelling, this is a pretty well
> known anti pattern.
>
> When rows get above a few 10’s  of MB things can slow down, when they get
> above 50 MB they can be a pain, when they get above 100MB it’s a warning
> sign. And when they get above 1GB, well you you don’t want to know what
> happens then.
>
> It’s a bad idea and you should take another look at the data model. If you
> have to do it, you can try the ByteOrderedPartitioner which uses the row
> key as a token, given you total control of the row placement.
>
> Cheers
>
>
> -----------------
> Aaron Morton
> New Zealand
> @aaronmorton
>
> Co-Founder & Principal Consultant
> Apache Cassandra Consulting
> http://www.thelastpickle.com
>
> On 4/12/2013, at 8:32 pm, Vivek Mishra <mishra.vivs@gmail.com> wrote:
>
> So Basically you want to create a cluster of multiple unique keys, but
> data which belongs to one unique should be colocated. correct?
>
> -Vivek
>
>
> On Tue, Dec 3, 2013 at 10:39 AM, onlinespending <onlinespending@gmail.com>wrote:
>
>> Subject says it all. I want to be able to randomly distribute a large set
>> of records but keep them clustered in one wide row per node.
>>
>> As an example, lets say I’ve got a collection of about 1 million records
>> each with a unique id. If I just go ahead and set the primary key (and
>> therefore the partition key) as the unique id, I’ll get very good random
>> distribution across my server cluster. However, each record will be its own
>> row. I’d like to have each record belong to one large wide row (per server
>> node) so I can have them sorted or clustered on some other column.
>>
>> If I say have 5 nodes in my cluster, I could randomly assign a value of 1
>> - 5 at the time of creation and have the partition key set to this value.
>> But this becomes troublesome if I add or remove nodes. What effectively I
>> want is to partition on the unique id of the record modulus N (id % N;
>> where N is the number of nodes).
>>
>> I have to imagine there’s a mechanism in Cassandra to simply randomize
>> the partitioning without even using a key (and then clustering on some
>> column).
>>
>> Thanks for any help.
>
>
>
>

Mime
View raw message